There are many cases in which, in an air conditioner, an inverter circuit for converting a direct current into an alternating current is used to supply an alternating current power to a motor which drives a compressor. In general, in the inverter circuit, a phase current detection device which detects a phase current of an output alternating current is provided for the purpose of controlling a current flowing in the motor, etc. (see, for example, PATENT DOCUMENT 1). A phase current detection device of PATENT DOCUMENT 1 includes a shunt resistor provided in a DC link, and an amplifier which receives a voltage across the shunt resistor and outputs a detection current, and detects a phase current using a voltage pulse generated at the shunt resistor while PWM control (PWM: pulse width modulation) is performed.
Incidentally, the above-described inverter circuit converts a direct current into an alternating current by changing respective switching states of a plurality of switching elements. Thus, if the frequency (the carrier frequency) of a carrier signal can be increased, responsiveness of output control can be improved (i.e., a control band can be increased). To realize the foregoing, for example, the switching speed has to be increased in the PWM control inverter circuit. For example, it is expected that the carrier frequency can be increased by increasing the switching speed (for example, to a speed ten times the switching speed of a conventional inverter circuit or higher) using a switching element made of wide bandgap semiconductor.